Set the default for -bbsections-cold-text-prefix to .text.split.

[snehasish]

Summary

After using this for a while, we find that it is generally useful to
have it set to .text.split. by default, removing the need for an
additional -mllvm option.

[snehasish]

Updated tests to use .text.split. prefix.

[tmsriram]

This LGTM as there is an option to keep it in ".text.unlikely" if desired. Please wait for Eric's response too. Thanks!

[MaskRay]

Please fix the comment in TargetLoweringObjectFileImpl.cpp:879

[snehasish]

Update comment and rebase.

[MaskRay]

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

870 ↗

(On Diff #297100)

.text.split -> .text.split.

[snehasish]

Update prefix to .text.split.

[snehasish]

Thanks for the review.

[snehasish]

Rebase.

llvm/lib/CodeGen/BasicBlockSections.cpp

 using llvm::SmallSet;
 using llvm::SmallVector;
 using llvm::StringMap;
 using llvm::StringRef;
 using namespace llvm;
 
 // Placing the cold clusters in a separate section mitigates against poor
 // profiles and allows optimizations such as hugepage mapping to be applied at a
-// section granularity. Where necessary, users should set this to ".text.split."
-// which is recognized by lld via the `-z keep-text-section-prefix` flag.
+// section granularity. Defaults to ".text.split." which is recognized by lld
+// via the `-z keep-text-section-prefix` flag.
 cl::opt<std::string> llvm::BBSectionsColdTextPrefix(
     "bbsections-cold-text-prefix",
     cl::desc("The text prefix to use for cold basic block clusters"),
-    cl::init(".text.unlikely."), cl::Hidden);
+    cl::init(".text.split."), cl::Hidden);
 
 namespace {
 
 // This struct represents the cluster information for a machine basic block.
 struct BBClusterInfo {
   // MachineBasicBlock ID.
   unsigned MBBNumber;
   // Cluster ID this basic block belongs to.

llvm/test/CodeGen/X86/basic-block-sections-clusters-branches.ll

 ; LINUX-SECTIONS1-LABEL:  foo:
 ; LINUX-SECTIONS1:    jne foo.1
 ; LINUX-SECTIONS1-NOT:    {{jne|je|jmp}}
 ; LINUX-SECTIONS1-LABEL:  # %bb.2:
 ; LINUX-SECTIONS1:    jmp foo.cold
 ; LINUX-SECTIONS1:    .section        .text.foo,"ax",@progbits,unique,1
 ; LINUX-SECTIONS1-LABEL:  foo.1:
 ; LINUX-SECTIONS1:    jmp foo.cold
-; LINUX-SECTIONS1:    .section        .text.unlikely.foo,"ax",@progbits
+; LINUX-SECTIONS1:    .section        .text.split.foo,"ax",@progbits
 ; LINUX-SECTIONS1-LABEL:  foo.cold:
 
 ; LINUX-SECTIONS2:    .section        .text.foo,"ax",@progbits
 ; LINUX-SECTIONS2-LABEL:  foo:
 ; LINUX-SECTIONS2:    jne foo.0
 ; LINUX-SECTIONS2-NOT:    {{jne|je|jmp}}
 ; LINUX-SECTIONS2-LABEL:  # %bb.2:
 ; LINUX-SECTIONS2:    jmp .LBB0_3
 ; LINUX-SECTIONS2:    .section        .text.foo,"ax",@progbits,unique,1
 ; LINUX-SECTIONS2:    foo.0:
 ; LINUX-SECTIONS2-NOT:    {{jne|je|jmp}}
 ; LINUX-SECTIONS2:    .LBB0_3:

llvm/test/CodeGen/X86/basic-block-sections-clusters.ll

 ; LINUX-SECTIONS1-NOT:    .LBB_END0_{{0-9}}+
 ; LINUX-SECTIONS1-LABEL:  # %bb.2:
 ; LINUX-SECTIONS1-NOT:    .LBB_END0_{{0-9}}+
 ; LINUX-SECTIONS1:    .section        .text.foo,"ax",@progbits,unique,1
 ; LINUX-SECTIONS1-LABEL:  foo.1:
 ; LINUX-SECTIONS1-LABEL:  .LBB_END0_1:
 ; LINUX-SECTIONS1-NEXT:        .size   foo.1, .LBB_END0_1-foo.1
 ; LINUX-SECTIONS1-NOT:    .section
-; LINUX-SECTIONS1:    .section        .text.unlikely.foo,"ax",@progbits
+; LINUX-SECTIONS1:    .section        .text.split.foo,"ax",@progbits
 ; LINUX-SECTIONS1-LABEL:  foo.cold:
 ; LINUX-SECTIONS1-LABEL:  .LBB_END0_3:
 ; LINUX-SECTIONS1-NEXT:        .size   foo.cold, .LBB_END0_3-foo.cold
 ; LINUX-SECTIONS1:      .section  .text.foo,"ax",@progbits
 ; LINUX-SECTIONS1-LABEL:  .Lfunc_end0:
 ; LINUX-SECTIONS1-NEXT:   .size foo, .Lfunc_end0-foo
 
 ; LINUX-SECTIONS2:    .section        .text.foo,"ax",@progbits

llvm/test/CodeGen/X86/basic-block-sections-cold.ll

 ; Check if basic blocks that don't get unique sections are placed in cold sections.
 ; Basic block with id 1 and 2 must be in the cold section.
 ; RUN: echo '!_Z3bazb' > %t
 ; RUN: echo '!!0' >> %t
 ; RUN: llc < %s -mtriple=x86_64 -function-sections -basic-block-sections=%t -unique-basic-block-section-names | FileCheck %s -check-prefix=LINUX-SECTIONS
-; RUN: llc < %s -mtriple=x86_64 -function-sections -basic-block-sections=%t -unique-basic-block-section-names -bbsections-cold-text-prefix=".text.split." | FileCheck %s -check-prefix=LINUX-SPLIT
+; RUN: llc < %s -mtriple=x86_64 -function-sections -basic-block-sections=%t -unique-basic-block-section-names -bbsections-cold-text-prefix=".text.unlikely." | FileCheck %s -check-prefix=LINUX-SPLIT
 
 define void @_Z3bazb(i1 zeroext %0) nounwind {
   br i1 %0, label %2, label %4
 
 2:                                                ; preds = %1
   %3 = call i32 @_Z3barv()
   br label %6
 

 
 declare i32 @_Z3foov() #1
 
 ; LINUX-SECTIONS: .section        .text._Z3bazb,"ax",@progbits
 ; LINUX-SECTIONS: _Z3bazb:
 ; Check that the basic block with id 1 doesn't get a section.
 ; LINUX-SECTIONS-NOT: .section        .text._Z3bazb._Z3bazb.1,"ax",@progbits,unique
 ; Check that a single cold section is started here and id 1 and 2 blocks are placed here.
-; LINUX-SECTIONS: .section  .text.unlikely._Z3bazb,"ax",@progbits
+; LINUX-SECTIONS: .section  .text.split._Z3bazb,"ax",@progbits
 ; LINUX-SECTIONS: _Z3bazb.cold:
 ; LINUX-SECTIONS-NOT: .section        .text._Z3bazb._Z3bazb.2,"ax",@progbits,unique
 ; LINUX-SECTIONS: .LBB0_2:
 ; LINUX-SECTIONS: .size   _Z3bazb, .Lfunc_end{{[0-9]}}-_Z3bazb
 
-; LINUX-SPLIT:      .section  .text.split._Z3bazb,"ax",@progbits
+; LINUX-SPLIT:      .section  .text.unlikely._Z3bazb,"ax",@progbits
 ; LINUX-SPLIT-NEXT: _Z3bazb.cold:
 ; LINUX-SPLIT-NEXT:   callq _Z3barv
 ; LINUX-SPLIT:      .LBB0_2:
 ; LINUX-SPLIT:      .LBB_END0_2: